A native Korean speaker says this is a very strange sentence. Koreans would be much more likely to say, "the man is very thirsty," or "the man needs a lot to drink." Personally, as a physician, I would say,
남자가 탈소 상태 예요.
[man] [dehydrated] [state] [is]. The man is dehydrated.
Hi, The first 는 modifies the verb 하다 and turns it into an adjective "that/who exercises" or "exercising". Notice that the verb comes before the noun 남자. The second 는 denotes the topic of the sentence - man. The 는 on 하다 thus has a different function from the 는 on 남자. I hope this helps. Native Korean speakers, please correct me if I have misunderstood.